Electrical conductivity on composite cylinder and cylinder housing

Technical field

This invention relates to the need of electrical conductivity for composite cylinders at applications where it is important to safely discharge electrical energy for users and end users. During the filling process of those cylinders, it is critical that potential electrical sparks from the filling nozzle when connected to the filling valve (1), are directly discharged to the ground in order to eliminate the possibility of explosion. After filament winding of the cylinder, the electrical connection (2) is introduced to the cylinder by several slopes, controlled by filament winding machine, beginning from the valve (1) to the bottom of the cylinder (3). After the cylinder is equipped with electrical materials such as wire and carbon fiber, it is then possible to connect, at any point of the cylinder surface, to the ground.

Background

Pressure cylinders have been manufactured for many decades from metal or steel without implementation of technical developments. Today, new materials, advanced technical standards, safety features and design changes allow replacement of existing gas cylinder design with composite cylinders. The mechanical properties are better than those of steel cylinders and the annual maintenance costs are much less. However, since most plastic materials are non conductive, these cylinders need either special treatment during filling or to be electrical conductive. Most composite cylinder manufacturers do not mention anything about electrical conductivity but they are using valves with different liquid gas distribution where the liquid gas runs,

during filling, on the cylinder wall into the cylinder and they recommend spraying the cylinder housing with water before filling. This method doesn't solve the electrical conductivity problem when the cylinder is at end user and the water makes the cylinder housing viable to dust.

In the Automotive Industry, the plastic fuel tank has almost replaced the steel tank because of its reduced weight, safety and maintenance free features. Each plastic fuel tank has its grounding wire connected at the filler neck to the car body in order to avoid any electrical sparks and the risk of explosion during pumping petrol. Today, the most common alternative fuels in use are LPG and CNG cylinder which gives the car the option to run either on petrol or gas. Since these cylinders are made of metal they automatically their have electrical ground through to the fixation on the car body.

Composite cylinder properties can be adjusted to their specific needs; they can have the same electrical properties as metal cylinders, wherever this is needed. Electrical conductive composite cylinders open a wide range of new applications like LPG and CNG gas cylinders for household and Automotive applications and all the areas where explosion proof equipment has to be used which requires electrical conductivity.

Disclosure of invention and summary

Fig. 1 shows the composite cylinder with electrical conductivity.

The present invention provides a method to manufacture filament wounded cylinders at high production speed and where the last winding along the cylinder is done with conductive material like (2) metal wire, carbon fiber roving, or similar electrical conductive material. The winding of the last roving starts at the cylinder valve (1) without resin and only after a few rounds around the valve, the resin will be introduced to the roving until the winding continues down to the bottom of the cylinder (3). The resin on the roving can be removed at certain points where the electrical connection to the ground is required. This means the entire cylinder length can be used for electrical grounding, if required. With this method, there are no design limitations for fixing the electrical ground to the cylinder and allows the areas of the roving, where the resin is not removed, to work as the plastic cover of a normal electrical wire. This invention provides for LPG and CNG cylinders, used as alternative fuels in the Automotive Industry, an easy-to-use solution for electrical grounding.

However, for LPG composite gas cylinders for use with cooking gas, the electrical conductivity has to be extended from the composite cylinder to the cylinder housing. The bottom part of the cylinder housing (5) is manufactured with conductive material and non conductive material. Fig. 2 shows where the conductive (5) and non conductive (6) materials in the housing are and how to have the final link to the ground (4). The composite LPG cylinder for use with cooking gas (with housing) can be filled and handled in the same way as the steel cylinder without additional special treatment. Manufacturing molds are designed in a way that they can distribute different materials to different locations on the product.

Function of invention and description of drawing

After the filament winding around the HDPE liner (8) is completed, the electrical conductive roving (2) (carbon fiber or similar conductive material) is wound around the metal insert (7) on the finished liner. The first few layers are without resin in order to create the electrical connection to the metal insert (7) in which the LPG valve (1) is screwed in. When the electrical connection (2) between the liner (3) and metal insert (7) is established, the roving (2) is introduced to the resin bath, wound several times around the metal insert (7) and then sloped down to the bottom of the composite cylinder (3). The bottom of the cylinder (3) has several electrical conductive roving layers. At predefined areas of the composite cylinder, the resin from the conductive roving (2) is removed in order to have areas of blank roving which are now the electrical connecting points to the cylinder housing (4, 5). The cylinder housing is injection molded with a two component injection molding machine. One component is HDPE and the other component is electrical conductive Plastic. The electrical conductive plastic is distributed from inside the bottom housing (5), where the holding points of the composite cylinder are, to the outside of the bottom housing into the outer layer (4) of the rolling ring. The rolling ring function is to enable the standing composite cylinder to be rolled on the edge of the rolling ring.

The advantage of this invention is that the composite cylinder is electrical conductive from the filling valve (1) along the entire composite cylinder and through the cylinder housing to the outside of the rolling ring. The composite cylinder has now the same electrical properties as a metal cylinder and no additional handling during filling or at the end user is required. For applications where the cylinder housing is not required (Automotive Industry, explosion proof areas, etc.) the cylinder has electrical connection points along its entire surface and the electrical ground connection can easily be established.